diff --git a/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java b/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java
index 8333b9cf029..fd7453aa380 100644
--- a/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java
+++ b/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java
@@ -1193,7 +1193,7 @@ public abstract class BlobStoreRepository extends AbstractLifecycleComponent imp
                             try {
                                 blobContainer().deleteBlobsIgnoringIfNotExists(oldIndexN);
                             } catch (IOException e) {
-                                logger.warn("Failed to clean up old index blobs {}", oldIndexN);
+                                logger.warn(() -> new ParameterizedMessage("Failed to clean up old index blobs {}", oldIndexN), e);
                             }
                         }));
                     }
diff --git a/test/fixtures/gcs-fixture/src/main/java/fixture/gcs/GoogleCloudStorageHttpHandler.java b/test/fixtures/gcs-fixture/src/main/java/fixture/gcs/GoogleCloudStorageHttpHandler.java
index 98b081a37e5..f0795968ff1 100644
--- a/test/fixtures/gcs-fixture/src/main/java/fixture/gcs/GoogleCloudStorageHttpHandler.java
+++ b/test/fixtures/gcs-fixture/src/main/java/fixture/gcs/GoogleCloudStorageHttpHandler.java
@@ -189,7 +189,8 @@ public class GoogleCloudStorageHttpHandler implements HttpHandler {
                     exchange.sendResponseHeaders(RestStatus.OK.getStatus(), response.length);
                     exchange.getResponseBody().write(response);
                 } else {
-                    exchange.sendResponseHeaders(RestStatus.BAD_REQUEST.getStatus(), -1);
+                    throw new AssertionError("Could not read multi-part request to [" + request + "] with headers ["
+                        + new HashMap<>(exchange.getRequestHeaders()) + "]");
                 }
 
             } else if (Regex.simpleMatch("POST /upload/storage/v1/b/" + bucket + "/*uploadType=resumable*", request)) {